Conventional silver halide color photographic elements contain a number of silver halide emulsion layers. These layers are spectrally sensitized to particular colors of light and have associated therewith coupler compounds capable of forming image dyes upon contact with oxidized developer. In order to obtain an image in a desirable processing time, it is necessary that the coupler have sufficient activity to form the image in the allowed processing time. This requires a certain minimum range of reactivity. When the image is ultimately comprised of more than one dye, it is further necessary that the reactivity of the couplers of different colors be balanced so as to enable a proper neutral color when needed.
When a coupler provides an image dye having desirable hue, the coupler is of no practical utility unless it is sufficiently reactive with oxidized developer to produce the desire maximum density in the desired time. Hydrophilic substituents on couplers have been used effectively to lower the apparent dispersion pKa (known as pH 1/2) of the coupler. They increase the hydrophilicity of the coupler/coupler solvent particles. However, such substituents may have adverse effects on other aspects of the couplers' performance. Couplers must have manufacturable syntheses, and yield dyes which absorb in the correct region of the visible spectrum and which are resistant to fading by light, heat and humidity. Also, the couplers must be active, have a low propensity to form fog, be easily dispersible and must themselves be resistant to the deleterious actions of light, heat and humidity.
U.S. Pat. No. 4,840,877 (Fuji) discloses the use of ballasted carboxylic acids with magenta dye forming couplers to improve the coupler performance. The acids reduce coupler/silver interactions which may lead to speed losses, and the acids improve the efficiency of dye formation.
U.S. Pat. No. 5,382,500 (Fuji) includes sulfonamides in green sensitive layers. Pyrazolotriazoles are coated in combination with at least one non-color forming compound which is either a sulfonamide or a phenol. These mixtures have improved keeping (less silver interaction under high temperature or/and high humidity conditions) and improved process pH sensitivity. The sulfonamide definition includes N- and S-substituents that are aryl groups and further that the N-substituent has a p-group that has Hammett .sigma..sub.p &gt;negative 0.4. In the examples, one structure has the N-substituent as 2,4,6-trichlorophenyl (.SIGMA..sigma..sub.p =0.69) and a phenyl rather than an alkyl S-substituent.
JP 07209839 A2 claims sulfonamides as development accelerators in heat-developable systems in combination with dye releasing reductants. The closest structure is of the form Ar--SO.sub.2 NH--Ar--(m-SO.sub.2 NHR).
U.S. Pat. No. 4,973,535 describes the use of sulfonamide solvents to alter the hue of couplers. Formula 2 (col. 4) includes C.sub.4 H.sub.9 SO.sub.2 NH-Ph-C.sub.2 H.sub.5 and Formula 4 includes C.sub.7 H.sub.15 SO.sub.2 NH-Ph-3,4-diCl (.SIGMA..sigma..sub.p =0.46).
U.S. Pat. No. 5,120,636 (Fuji) discloses a combination of a magenta coupler, solvent and a bis-phenol for improved light fastness. The solvent general structure includes sulfonamides where one or both substituents can be aryl. The example structures are all high pKa sulfonamides.
A problem to be solved is to find an addenda compound that will improve the reactivity of a coupler when the reactivity is otherwise unacceptable.